There are many applications that require a linear actuator to both move at high speed with low force, and at low speed with high force. An example application might be a nailing machine, or a riveting or metal pressing machine. The desired machine would rapidly move the ram or rod of the linear actuator with high speed to the point where high force is needed. This first part of the cycle does not itself require high force. This first part of the cycle is typically followed by a need for a short stroke at high force (to insert a rivet or a nail for example). There are other applications that may require a different sequence of high speed and high force moves, but many of these are similar in that a single actuator needs to perform both types of motion.
For a linear actuator to meet both the high speed and high force (or torque) requirements using a single motor, the motor must be capable of high power (power is proportional to speed×force for linear motion, or proportional to rpm×torque for the motor's rotary input to a screw type actuator). A high power motor will generally cost more and be larger than a lower power motor, and if drive electronics are required, their cost and size will also typically be greater as power is increased.
One solution to this problem is to use separate actuators, one for high force and another for high speed applications. Another solution might be to use a transmission of some sort to change the output of a motor from low torque and high speed to high torque and low speed, perhaps with a two-speed gear box, or a continuously variable belt drive transmission (CVT) for example. These solutions can require expensive or complicated mechanisms, and often require active electronic control. These solutions may require speed changes or stoppage of the actuator (from what would otherwise be a continuous motion) to implement a torque change, or may require sensing the load change to actively shift speeds, or to actuate a shift mechanism in a transmission, or to programmatically actuate a change in a CVT ratio at a given actuator location in temporal anticipation of a load increase at a given location, or to otherwise control the system.
Therefore, there is a need in the art for a method, apparatus and system for driving a linear actuator with two motors via a transmission in order to provide both high speed and high force or torque as needed. The invention should also preferably overcome the drawbacks associated with the foregoing systems and methods. Aspects of the present invention overcome these and other shortcomings of the prior art and address these needs in the art.